The present invention relates to a method for manufacturing a plasma display panel and the plasma display panel.
Plasma display panels (hereafter abbreviated as PDPs) can be roughly divided into direct current (DC) types and alternating current (AC) types. At present, AC types, which are suited to upsizing of the panel, are prevalent.
The AC type PDP is composed of a front glass substrate and a back glass substrate which are disposed to face each other with partition walls in between. On the facing surface of the front glass substrate, a plurality of parallel display electrodes are provided, while on the facing surface of the back glass substrate, a plurality of address electrodes are provided orthogonal to the display electrodes. Red, green, or blue phosphors are each laid down in a discharge space formed by dividing the gap between both substrates by the partition walls and each space is filled with a discharge gas so as to form each colored light emitting cell.
In the PDP having the above-described structure, electric discharge is induced in each cell by applying a voltage to the corresponding electrode via the driving circuit, so that ultraviolet light is emitted. Then, phosphor particles included in the phosphors (red, green, and blue) are excited by the ultraviolet light to emit light.
The display electrode is composed of a metal layer such as Ag, or composed of lamination of a metal layer 522 such as Ag, Cu, or Cr formed on an ITO (Indium Tin Oxide) layer 521 as shown in FIG. 10. Such construction is generally formed by the methods shown in FIGS. 11A and 11B.
According to the method shown in FIG. 11A, an Ag electrode is formed by the photolithography method. In this method, the Ag electrode is formed by applying a photosensitive Ag paste on the glass substrate, exposing the photosensitive Ag paste to light through a mask, developing and baking it.
According to the method shown in FIG. 11B, lamination of Cr/Cu/Cr layers disposed on an ITO layer which makes up an electrode is formed by the photolithography method. In this method, the electrode is formed by depositing the ITO layer and the lamination of Cr/Cu/Cr by sputtering in this order and etching these layers.
However, the electrode made of Ag would cause a problem of yellowing in the glass substrate, and the electrode made of Cr/Cu/Cr would cause a problem of making the glass substrate blue because of Cu contained therein. Especially, the yellowing due to Ag would lead to degradation in color purity of emitted light. This problem occurs as follows. That is, Ag (specifically, Ag ions) in the electrode diffuses into the glass substrate and the dielectric layer during the baking steps of the electrode and the dielectric layer, and the diffused Ag ions are reduced by Sn, Na, and Pb ions contained in the glass substrate, so that Ag colloidal particles are precipitated.
In addition, the baking step of the electrode would lead to shrinkage of the electrode, which generates residual stresses in the finished electrode and so the electrode or the substrate itself would become deformed. Such deformation might result in reduction in the yields of the panels and increase in the cost of manufacturing the panels. Especially, this problem becomes remarkably serious for forming thick film electrodes with high definition patterns which are recently required for high-definition TVs.
Meanwhile, according to the method shown in FIG. 11B, it takes a long time to form a thick metal layer.
To cope with the above-mentioned problems, the Japanese Patent Publication No.3107018 discloses that an metal electrode is formed on the surface of the base layer disposed on the substrate by electroplating. According to this method, in order to give the plating only to the area where the metal electrode will be formed, a resist mask is formed on the other area by photolithography. Since such a method dispenses with the baking step of the electrode and so there is no problem of yellowing, the method is favorable for increasing the yields. However, the base layer has to have electrical conductivity, which causes a problem that materials available as the base layer are limited. Additionally, this method requires a step for forming the resist mask on the area where the electrode will not be formed, which makes the method more complicated.
In view of the above-described problems, the object of the invention is to provide a method for manufacturing a high-luminance and high-image-quality plasma display panel reduced in yellowing, and a plasma display panel obtained by the method.
In order to achieve the above object, a method for manufacturing a plasma display panel according to the invention includes a first electrode formation step for forming a plurality of first electrodes on a surface of a first substrate, a second electrode formation step for forming a plurality of second electrodes on a surface of a second substrate, and a substrate alignment step for aligning the first and the second substrates so as to face each other. Here, at least one of the first electrode formation step and the second electrode formation step includes the following substeps: a base layer formation substep for forming a base layer on the surface of the substrate; a precipitation promoting substep for conducting a procedure for promoting a precipitation reaction of a metal material at a region in the base layer where a metal layer will be formed; and a metal layer formation substep for forming the metal layer at the region by an electroless plating method, during or after the procedure in the precipitation promoting step.
Note here that, although the base layer may be conductors or insulators, the base layer using a conductor has to be accompanied with patterning of the layer.
With this method, since the metal layer is formed using the electroless plating method, it becomes easy to form an electrode with a thick film. Additionally, since there is no need to bake the electrode in the formation step thereof, thus formed electrode is not subject to residual stresses, while yellowing in the panel can be prevented.
In addition, the metal layer is formed following the procedure for promoting the precipitation reaction of the metal material. Therefore, thus formed metal layer is dense and has strong adhesion to the base layer. Note here that the precipitation promoting procedure may be conducted before the metal formation step, or in parallel with the metal formation step.
With this method, the metal layer can be selectively formed only on the required regions without using a resist mask.
Further, the laminated construction in which the base layer containing the metal oxide and the metal layer such as Ag are laminated on the substrate in this order can prevent yellowing in the panel. This is because the base layer prevents diffusion of metal ions from the metal layer into the substrate.
With reference to the procedure for promoting the precipitation reaction of the metal material, a catalyst for promoting the reaction is preferably deposited on the regions.
The catalyst is preferably palladium.
The catalyst can be deposited on the regions by immersing the substrate with the base layer thereon in an acid aqueous solution containing palladium and radiating light to the regions through the aqueous solution.
The acid aqueous solution containing palladium is preferably a palladium nitrate aqueous solution or a palladium acetate aqueous solution. This is because these solution can realize higher deposit density of palladium as compared with a palladium hydrochloride aqueous solution.
With this method, the patterning of the base layer can be made by selectively removing the portions of the base layer to which light is not radiated. That is, in the regions on which palladium is deposited, the palladium functions as a protective film so that the regions are not removed. Meanwhile, other regions on which the palladium is not deposited are removed.
Alternatively, palladium can be deposited on the regions by forming a resist film with a predetermined pattern on the base layer, depositing palladium on the base layer by sputtering, and then removing the resist film.
Next, the method for forming the metal layer on the regions without using a catalyst such as palladium will be described in the paragraphs that follow.
The precipitation promoting step and the metal formation step are concurrently performed. In these steps, the substrate on which the base layer is formed is immersed in an electroless plating solution, and light is radiated to the regions through a mask, so that the metal layer is formed on the regions.
This method makes use of a reduction precipitation reaction of the metal, which is caused by electrons excited by the radiated light through the medium of the electroless plating solution.
The base layer is preferably made of a metal oxide in terms of adhesion to the substrate and prevention against diffusion of metal ions into the substrate.
In the base layer formation step, a photosensitive film containing a metal or metal oxides is formed on the substrate, which is followed by development and etching processes, so that the base layer with a predetermined pattern can be formed on predetermined regions without using a resist film.
As for the photosensitive film, a gel film obtained by providing heat treatment for a sol film generated from a metal alkoxide substituted with a xcex2-diketone chelate class or an organic polysilane film containing a metal oxide and a metal alkoxide can be used.
Since these films are clear and colorless, they are suitable for the base layer.
The base layer can be also formed by sputtering, a CVD method, dip-coating, a spray pyrolysis method, and the like.
The metal oxide is preferably made of one or more metal oxides selected out of nickel oxide, cobalt oxide, iron oxide, zinc oxide, indium oxide, copper oxide, titanium oxide, praseodymium oxide, and silicon oxide.
The method for manufacturing the PDP according to another embodiment of the invention includes a first electrode formation step for forming a plurality of first electrodes on a surface of a first substrate, a second electrode formation step for forming a plurality of second electrodes on a surface of a second substrate, and a substrate alignment step for aligning the first and the second substrates so as to face each other. Here, at least one of the first electrode formation step and the second electrode formation step includes the following substeps of: a base layer formation substep for forming a base layer at a region on the surface of the substrate where a metal layer will be formed, the base layer having higher precipitation reactivity of the metal than the surface of the substrate; and a metal layer formation substep for forming the metal layer on the base layer by an electroless plating method.
With this method, the metal layer is formed principally all over the base layer. Thus formed base layer can prevent yellowing in the panel in the same way as in the above-described method. Also, the metal layer is dense and has strong adhesion to the base layer.
Note here that the base layer can be formed, as previously mentioned, by patterning the metal oxide layer and depositing palladium all over the surface of the base layer. However, this method is preferable to such a method using palladium, because ZnO can function as the substitution for palladium. This is because the surface of the layer made of ZnO presents favorable precipitation reactivity of the metal material during the electroless plating.
More specifically, the ZnO layer is preferably made by forming a ZnO film all over the surface of the substrate using a thermal CVD method or a plasma CVD method, forming a resist film on regions of the ZnO film where the metal layer will be formed, which is followed by an etching process, and then removing the resist film.
When the thermal CVD method or the plasma CVD method is used for forming the ZnO film, thus obtained ZnO film has stronger adhesion to the substrate as compared with the film using the spray pyrolysis method and the like.
The above-mentioned methods are suitable for manufacturing PDPs whose first electrodes each consist of a plurality of line portions.
Further, a PDP according to the invention includes a first substrate on which a plurality of first electrodes are formed, a second substrate on which a plurality of second electrodes are formed, where the first and the second electrodes face each other. In the PDP, at least the first electrodes or the second electrodes have a construction in which a metal layer is laminated on a layer containing a metal oxide, and palladium is deposited at the interface between the layer containing the metal oxide and the metal layer.
The PDP having the above construction has electrodes being dense and having strong adhesion to the substrate, and is reduced in panel yellowing.
The metal oxide used for the PDP is preferably made of one or more metal oxides selected out of nickel oxide, cobalt oxide, iron oxide, zinc oxide, indium oxide, copper oxide, titanium oxide, praseodymium oxide, and silicon oxide.